1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus and an electrophotographic image forming method. In particular, the present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a multi-function peripheral with functions of such devices in combination and a method of forming images using the image forming apparatus.
2. Description of the Related Art
An electrophotographic, monochrome image forming apparatus forms single color toner images on a photosensitive member. The toner images are transferred onto a sheet material passing through a nipping region defined between the photosensitive member and a transfer roller. Not all the toner particles are transferred onto the sheet material and a part of the toner particles remains on the photosensitive member without being transferred. In order to remove the residual toner particles from the photosensitive member, a method is proposed in which a cleaning member is provided in contact with the surface of the photosensitive member to remove the toner particles therefrom.
A variety of full color image forming apparatuses have been proposed so far. Among other things, one of the proposed electrophotographic, full color image forming apparatus is designed to transfer the toner images on the photosensitive member onto an intermediate transfer belt passing through a nipping region defined between the photosensitive member and a first transfer roller. The toner images are then transferred onto the sheet material passing through a second nipping region defined between the intermediate transfer belt and a second transfer roller. The residual toner particles on the intermediate transfer belt are removed by a cleaning member provided in contact with the photosensitive member.
Conventionally, the cleaning member for removing residual toner particles from the photosensitive member and the intermediate transfer belt is made of rubber blade or rotatable brush. For example, JP 2004-310060 A discloses a cleaning device with a cleaning member made of rotatable brush for the cleaning of the intermediate transfer belt.
As shown in FIG. 13, the cleaning device disclosed in JP 2004-310060 A includes a cleaning brush 142 provided in contact with the intermediate transfer belt 130, a charging brush 174 also provided in contact with the intermediate transfer belt 130 on the upstream side from the cleaning brush 142 with reference to the moving direction of the intermediate transfer belt (counterclockwise direction in the drawing), a collecting roller 177 provided in contact with the cleaning brush 142, and a scraper 178 provided in contact with the collecting roller 177. A power supply 184 is connected to the scraper 178, and the charging brush 174 is grounded. With the arrangement, when the power supply 184 is turned on, electric current flows from the power supply 184 to the scraper 178 through the scraper 178, the collecting roller 177, the cleaning brush 142, the intermediate transfer belt 130, and the charging brush 174. This results in that most of the toner particles on the intermediate transfer belt 177 are electrically charged into a negative polarity. The negatively charged toner particles are then transported by the rotation of the belt 130 in the contact region of the cleaning brush 142 and the intermediate belt 130 where they are electrically attracted by the cleaning brush 142 and then removed from the intermediate transfer belt 177.
According to this arrangement, the toner particles not negatively charged between the intermediate transfer belt 130 and the charging brush 174 may be electrostatically and/or mechanically collected by and accumulated between the bristles of the brush 174. The accumulated toner particles may be transferred from the brush 174 due to, for example, vibrations caused by the engagements of the bristles with the rotating belt 130 and then adhere to the outer periphery of the belt 130. The toner particles adhered on the imaging region of the intermediate transfer belt can be transferred at the second transfer region onto the sheet material to deteriorate the resultant image quality. On the other hand, the toner particles adhered on the non-imaging region of the intermediate transfer belt can be transferred to the second transfer belt, which in turn is transferred onto the opposite surface of the sheet material.
In order to prevent the toner particles from being transferred onto the sheet material, before forming toner images, the intermediate transfer belt 130 may be circulated a full turn to transport the toner particles on the intermediate transfer belt into the contact region between the intermediate transfer belt 130 and the charging brush 174 where the toner particles are electrically charged and then removed by the subsequent contact with the cleaning brush, which disadvantageously delays the start of the image forming operation.